Plasma surface treatment of silicone hydrogel contact lenses

ABSTRACT

The present invention provides a method for treating a contact lens to provide an optically clear, hydrophilic coating upon the surface of a silicone hydrogel lens by subjecting the surface of the lens to a process comprising plasma treatment, hydration, and heat sterilization that is controlled to result in a silicate-containing film having a mosaic pattern of projecting plates surrounded by fissures when viewing a 50×50 micron square AFM image, wherein the peak-to-valley distances of the fissures are on average between about 100 and 500 angströms and the plate coverage is on average between about 40% to 99%.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of U.S. application Ser. No.09/295,675, filed Apr. 21, 1999.

FIELD OF THE INVENTION

[0002] The present invention is directed to the surface treatment ofsilicone hydrogel contact lenses. In particular, the present inventionis directed to a method of modifying the surface of a contact lens toincrease its wettability and to decrease its susceptibility to proteinand lipid deposition during use. The surface treatment results in asilicate-containing surface film or coating having a mosaic pattern ofraised plates surrounded by receding spaces or fissures. When viewing a50×50 micron square AFM image of the surface, the peak-to-valleydistances of the fissures are on average between about 100 and 500angströms and the plate coverage is on average between about 40% to 99%.

BACKGROUND

[0003] Contact lenses made from silicone-containing materials have beeninvestigated for a number of years. Such materials can generally besubdivided into two major classes, namely hydrogels and non-hydrogels.Non-hydrogels do not absorb appreciable amounts of water, whereashydrogels can absorb and retain water in an equilibrium state.Regardless of their water content, both non-hydrogel and hydrogelsilicone contact lenses tend to have relatively hydrophobic,non-wettable surfaces.

[0004] Those skilled in the art have long recognized the need formodifying the surface of such silicone contact lenses so that they arecompatible with the eye. It is known that increased hydrophilicity ofthe contact lens surface improves the wettability of the contact lenses.This in turn is associated with improved wear comfort of contact lenses.Additionally, the surface of the lens can affect the lens'ssusceptibility to deposition, particularly the deposition of proteinsand lipids from the tear fluid during lens wear. Accumulated depositioncan cause eye discomfort or even inflammation. In the case of extendedwear lenses, the surface is especially important, since extended wearlens must be designed for high standards of comfort over an extendedperiod of time, without requiring daily removal of the lens beforesleep. Thus, the regimen for the use of extended wear lenses would notprovide a daily period of time for the eye to recover from anydiscomfort or other possible adverse effects of lens wear.

[0005] Silicone lenses have been subjected to plasma surface treatmentto improve their surface properties, e.g., surfaces have been renderedmore hydrophilic, deposit resistant, scratch resistant, or otherwisemodified. Examples of previously disclosed plasma surface treatmentsinclude subjecting contact lens surfaces to a plasma comprising an inertgas or oxygen (see, for example, U.S. Pat. Nos. 4,055,378; 4,122,942;and 4,214,014); various hydrocarbon monomers (see, for example, U.S.Pat. No. 4,143,949); and combinations of oxidizing agents andhydrocarbons such as water and ethanol (see, for example, WO 95/04609and U.S. Pat. No 4,632,844). U.S. Pat. No. 4,312,575 to Peyman et al.discloses a process for providing a barrier coating on a silicone orpolyurethane lens by subjecting the lens to an electrical glow discharge(plasma) process conducted by first subjecting the lens to a hydrocarbonatmosphere followed by subjecting the lens to oxygen during flowdischarge, thereby increasing the hydrophilicity of the lens surface.

[0006] Although such surface treatments have been disclosed formodifying the surface properties of silicone contact lenses, the resultshave been problematic and of questionable commercial viability, whichhas no doubt contributed to the fact that silicone hydrogel contact lenshave yet to be commercialized. For example, U.S. Pat. No. 5,080,924 toKamel et al. states that although exposing the surface of an object toplasma discharge with oxygen is known to enhance the wettability orhydrophilicity of such surface, such treatment is only temporary.

[0007] Although the prior art has attempted to show that the surfacetreatment of contact lenses in the unhydrated state can be accomplished,there has been little or no discussion of the possible effect ofsubsequent processing or manufacturing steps on the surface treatment ofthe lens and no teaching or description of the surface properties of afully processed hydrogel lens manufactured for actual wear. Similarly,there has been little or no published information.

[0008] Thus, it is desired to provide a silicone hydrogel contact lenswith an optically clear, hydrophilic surface film that will not onlyexhibit improved wettability, but which will generally allow the use ofa silicone hydrogel contact lens in the human eye for extended period oftime. In the case of a silicone hydrogel lens for extended wear, itwould be highly desirable to provide a contact lens with a surface thatis also highly permeable to oxygen and water. Such a surface treatedlens would be comfortable to wear in actual use and would allow for theextended wear of the lens without irritation or other adverse effects tothe cornea. It would be desirable if such a surface treated lens were acommercially viable product capable of economic manufacture.

SUMMARY OF THE INVENTION

[0009] The present invention is directed to a silicone hydrogel lenswith a silicate-containing surface film having a mosaic pattern ofprojecting plates surrounded by receding spaces or fissures when viewinga 50-by-50 micron square AFM (Atomic Force Microscopy) image in whichthe average peak-to-valley distance (or average depth) of the fissuresis between about 100 and 500 angströms and the plate coverage is onaverage of about 40% to 99%. The present invention is also directed to amethod of modifying the surface of a contact lens to increase itswettability and to increase its resistance to the formation of depositsduring wear. The surface film can be made by oxidative plasma treatmentof the lens under suitable plasma conditions followed by hydration andautoclaving.

BRIEF DESCRIPTION OF DRAWINGS

[0010]FIG. 1 is a flow chart of a manufacturing process for making alens having a lens coating according to the present invention.

[0011]FIG. 2 is an Atomic Force Microscopy (AFM) topographical image(50×50 microns) showing a plasma-treated lens before further processingby extraction, hydration and sterilization according to the presentinvention.

[0012]FIG. 3 is an Atomic Force Microscopy (AFM) topographical image(50×50 square microns) showing, for comparison, a hydrated andautoclaved plasma-treated lens (fully processed) after a time period ofonly 4 minutes, otherwise processed comparably to the lens in FIG. 3,showing a relatively smooth surface with barely visable plates and about20 percent surface coverage.

[0013]FIG. 4 is an Atomic Force Microscopy (AFM) topographical image(50×50 microns) showing a plasma-treated lens according to the presentinvention that has been extracted with isopropanol and prior toautoclaving, showing about 50 percent surface coverage.

[0014]FIG. 5 is an Atomic Force Microscopy (AFM) topographical image(50×50 microns) showing a hydrated and autoclaved plasma-treated lens(fully processed) according to the present invention, after a timeperiod of 8 minutes per side according to the conditions of Example 1,showing about 95% surface coverage. All AFM images are on dried samples.

DETAILED DESCRIPTION OF THE INVENTION

[0015] As mentioned above, the present invention is directed to asilicone hydrogel contact lens having a silicate-containing coating anda method of manufacturing the same, which coating improves thehydrophilicity and lipid/protein resistance of the lens. Thus, thesilicate-containing coating allows a lens that could otherwise not becomfortably worn in the eye to be worn in the eye for an extended periodof time, for more than 24 hours at a time.

[0016] The surface treatment of silicone hydrogel lenses is complicatedby the fact that, although silicone hydrogel lenses may be plasmatreated in an unhydrated state, such lenses, unlike their non-hydrogelcounterparts, are subsequently swollen by solvent extraction andhydration, which can cause the dimensions of the lens to substantiallychange after coating. In fact, hydration may cause the lens to swellfrom about 10 to more than about 20 percent or more, depending upon theultimate water content of the lens. In addition to lens swelling duringsolvent extraction and hydration, the subsequent autoclaving of thehydrated lens, a common form of sterilizing lenses during themanufacture of packaged lenses, has also been found to substantiallyaffect the plasma modified lens surface. The present invention isdirected to a surface-modified silicone hydrogel lens having asilicate-containing coating that exhibits desirable coatingcharacteristics, even after the lens has been extracted, hydrated, andautoclaved.

[0017] In particular, a silicone hydrogel contact lens is provided witha silicate-containing coating that displays a mosaic-like pattern ofrelatively flat plates surrounded and separated by relatively narrowspaces or fissures wherein (i) the plates provide a surface coverage onaverage of between about 40 percent to 99 percent, and (ii) the fissureshave a peak-to-valley distance on average of between 100 and 500angströms. These coating characteristics of a fully-processed lens,following surface treatment, hydration, and sterilization, can beobserved and determined when viewing a 50×50 square micron image underAtomic Force Microscopy (AFM) as described in detail below.

[0018] The invention is applicable to a wide variety of siliconehydrogel contact lens materials. Hydrogels in general are a well knownclass of materials which comprise hydrated, cross-linked polymericsystems containing water in an equilibrium state. Silicone hydrogelsgenerally have a water content greater than about 5 weight percent andmore commonly between about 10 to about 80 weight percent. Suchmaterials are usually prepared by polymerizing a mixture containing atleast one silicone-containing monomer and at least one hydrophilicmonomer. Typically, either the silicone-containing monomer or thehydrophilic monomer functions as a crosslinking agent (a crosslinkerbeing defined as a monomer having multiple polymerizablefunctionalities) or a separate crosslinker may be employed. Applicablesilicone-containing monomeric units for use in the formation of siliconehydrogels are well known in the art and numerous examples are providedin U.S. Pat. Nos. 4,136,250; 4,153,641, 4,740,533; 5,034,461; 5,070,215;5,260,000; 5,310,779; and 5,358,995.

[0019] Examples of applicable silicon-containing monomeric units includebulky polysiloxanylalkyl (meth)acrylic monomers. An example of bulkypolysiloxanylalkyl (meth)acrylic monomers are represented by thefollowing Formula I:

[0020] wherein:

[0021] X denotes —O— or —NR—;

[0022] each R₁₈ independently denotes hydrogen or methyl;

[0023] each R₁₉ independently denotes a lower alkyl radical, phenylradical or a group represented by

[0024]  wherein each R₁₉′ independently denotes a lower alkyl or phenylradical; and

[0025] his 1 to 10.

[0026] Some preferred bulky monomers are methacryloxypropyltris(trimethyl-siloxy)silane or tris(trimethylsiloxy)silylpropylmethacrylate, sometimes referred to as TRIS, andtris(trimethylsiloxy)silylpropyl vinyl carbamate, sometimes referred toas TRIS-VC.

[0027] Another class of representative silicon-containing monomersincludes silicone-containing vinyl carbonate or vinyl carbamate monomerssuch as: 1,3-bis[4-vinyloxycarbonyloxy)but-1-yl]tetramethyl-disiloxane;3-(trimethylsilyl)propyl vinyl carbonate;3-(vinyloxycarbonylthio)propyl-[tris(trimethylsiloxy)silane];3-[tris(tri-methylsiloxy)silyl] propyl vinyl carbamate;3-[tris(trimethylsiloxy)silyl] propyl allyl carbamate;3-[tris(trimethylsiloxy)silyl]propyl vinyl carbonate;t-butyldimethylsiloxyethyl vinyl carbonate; trimethylsilylethyl vinylcarbonate; and trimethylsilylmethyl vinyl carbonate.

[0028] An example of silicon-containing vinyl carbonate or vinylcarbamate monomers are represented by Formula II:

[0029] wherein:

[0030] Y′ denotes —O—, —S— or —NH—;

[0031] R^(Si) denotes a silicone-containing organic radical;

[0032] R₂₀ denotes hydrogen or methyl;

[0033] d is 1, 2, 3 or 4;and q is 0or 1.

[0034] Suitable silicone-containing organic radicals R^(Si) include thefollowing:

—(CH₂)_(n′)Si[(CH₂)_(m′)CH₃]₃;

—(CH₂)_(n′)Si[OSi(CH₂)_(m′)CH₃]₃;

[0035]

[0036] wherein:

[0037] R₂₁ denotes

[0038] wherein p′ is 1 to 6;

[0039] R₂₂ denotes an alkyl radical or a fluoroalkyl radical having 1 to6 carbon atoms;

[0040] e is 1 to 200; n′ is 1, 2, 3 or 4; and m′ is 0, 1, 2, 3, 4 or 5.

[0041] An example of a particular species within Formula II isrepresented by Formula III.

[0042] Another class of silicon-containing monomers includespolyurethane-polysiloxane macromonomers (also sometimes referred to asprepolymers), which may have hard-soft-hard blocks like traditionalurethane elastomers. They may be end-capped with a hydrophilic monomersuch as HEMA. Examples of such silicone urethanes are disclosed in avariety or publications, including Lai, Yu-Chin, “The Role of BulkyPolysiloxanylalkyl Methacryates in Polyurethane-Polysiloxane Hydrogels,”Journal of Applied Polymer Science, Vol. 60, 1193-1199 (1996). PCTPublished Application No. WO 96/31792 discloses examples of suchmonomers, which disclosure is hereby incorporated by reference in itsentirety. Further examples of silicone urethane monomers are representedby Formulae IV and V:

(IV) E(*D*A*D*G)_(a)*D*A*D*E′; or

(V) E(*D*G*D*A)_(a)*D*G*D*E′;

[0043] wherein:

[0044] D denotes an alkyl diradical, an alkyl cycloalkyl diradical, acycloalkyl diradical, an aryl diradical or an alkylaryl diradical having6 to 30 carbon atoms;

[0045] G denotes an alkyl diradical, a cycloalkyl diradical, an alkylcycloalkyl diradical, an aryl diradical or an alkylaryl diradical having1 to 40 carbon atoms and which may contain ether, thio or amine linkagesin the main chain;

[0046] * denotes a urethane or ureido linkage;

[0047] a is at least 1;

[0048] A denotes a divalent polymeric radical of Formula VI:

[0049] wherein:

[0050] each R_(s) independently denotes an alkyl or fluoro-substitutedalkyl group having 1 to 10 carbon atoms which may contain ether linkagesbetween carbon atoms;

[0051] m′ is at least 1; and

[0052] p is a number which provides a moiety weight of 400 to 10,000;

[0053] each of E and E′ independently denotes a polymerizableunsaturated organic radical represented by Formula VII:

[0054] wherein:

[0055] R₂₃ is hydrogen or methyl;

[0056] R₂₄ is hydrogen, an alkyl radical having 1 to 6 carbon atoms, ora —CO—Y—R₂₆ radical wherein Y is —O—, —S— or —NH—;

[0057] R₂₅ is a divalent alkylene radical having 1 to 10 carbon atoms;

[0058] R₂₆ is a alkyl radical having 1 to 12 carbon atoms;

[0059] X denotes —CO— or —OCO—;

[0060] Z denotes —O— or —NH—;

[0061] Ar denotes an aromatic radical having 6 to 30 carbon atoms;

[0062] w is 0 to 6; x is 0 or 1; y is 0 or 1; and z is 0 or 1.

[0063] A more specific example of a silicone-containing urethane monomeris represented by Formula (VIII):

[0064] wherein m is at least 1 and is preferably 3 or 4, a is at least 1and preferably is 1, p is a number which provides a moiety weight of 400to 10,000 and is preferably at least 30, R₂₇, is a diradical of adiisocyanate after removal of the isocyanate group, such as thediradical of isophorone diisocyanate, and each E″ is a group representedby:

[0065] A preferred silicone hydrogel material comprises (in the bulkmonomer mixture that is copolymerized) 5 to 50 percent, preferably 10 to25, by weight of one or more silicone macromonomers, 5 to 75 percent,preferably 30 to 60 percent, by weight of one or more polysiloxanylalkyl(meth)acrylic monomers, and 10 to 50 percent, preferably 20 to 40percent, by weight of a hydrophilic monomer. In general, the siliconemacromonomer is a poly(organosiloxane) capped with an unsaturated groupat two or more ends of the molecule. In addition to the end groups inthe above structural formulas, U.S. Pat. No. 4,153,641 to Deichert etal. discloses additional unsaturated groups, including acryloxy ormethacryloxy. Preferably, the silane macromonomer is asilicon-containing vinyl carbonate or vinyl carbamate or apolyurethane-polysiloxane having one or more hard-soft-hard blocks andend-capped with a hydrophilic monomer.

[0066] Suitable hydrophilic monomers for use in silicone hydrogelsinclude, for example, unsaturated carboxylic acids, such as methacrylicand acrylic acids; acrylic substituted alcohols, such as2-hydroxyethylmethacrylate and 2-hydroxyethylacrylate; vinyl lactams,such as N-vinyl pyrrolidone; and acrylamides, such as methacrylamide andN,N-dimethylacrylamide. Still further examples are the hydrophilic vinylcarbonate or vinyl carbamate monomers disclosed in U.S. Pat. No.5,070,215, and the hydrophilic oxazolone monomers disclosed in U.S. Pat.No. 4,910,277. Other suitable hydrophilic monomers will be apparent toone skilled in the art.

[0067] Preferably, the lens material used in the present invention isnon-fluorinated or has relatively little fluorine atoms. Although thefluorination of certain monomers used in the formation of siliconehydrogels has been indicated to reduce the accumulation of deposits oncontact lenses made therefrom, highly fluorinated materials, because oftheir particular chemical nature, cannot be used to produce thesilicate-containing coatings according to the present invention. Thepresent invention is also not applicable to fumaride siloxane hydrogelcompositions according to U.S. Pat. No. 5,420,324. Without wishing to bebound by theory, it is surmised that the surface silicon content offumaride siloxane lenses is too high for the formation of a sufficientlyflexible silicate material, so that the silicate surface formed byoxidative plasma treatment is too glass-like, delaminating duringsubsequent processing. The silicon content of the surface layer beingtreated may be either a result of the bulk chemistry of the composition,including its hydrophobic and hydrophilic portions, and/or a result of asurface layering phenomenon resulting in a relative enrichment of layerswith respect to different monomers or elements.

[0068] Without wishing to be bound by theory, it is believed that thedesired coating, in a fully processed coating according to the presentinvention, has sufficient silicate content to provide the desiredsurface properties, such as wettability and deposition resistance, andsufficient polymer content to allow sufficient flexibility duringswelling and sufficient interfacial cohesion during heat sterilizationto prevent delamination. The relative balance, in the coating, ofhydrophobic and hydrophilic portions may also affect the coating'sresistance to delamination during thermal and hydrodynamic expansion orstress. In general, the hydrodynamic expansion of hydrogels in water isa function of the type and amount of the hydrophilic polymer content;and the thermal expansion is a function of the silicone polymer content.If the first increases, the second may decrease, or vice versa.

[0069] Thus, the chemistry of the silicate-containing coating or film inthe final product is not completely made of silicate and some of theoriginal material may remain in modified form. However, in general thecoating formed by plasma treatment, the original polymeric character ofthe material is changed to a more glass-like, hard material.

[0070] To determine the applicability of the present invention to aparticular silicone hydrogel material, the lens can be treated under twowidely diverse plasma set of conditions, a first “low and slow” plasmatreatment and a second “hot and fast” plasma treatment. If following thesteps of plasma treatment, hydration, and heat sterilization (so-called“full processing”), a silicate coating can be obtained, then somefurther adjustment of the process conditions should be able to achieve alens coating having surface characteristics according to the presentinvention. In general, a “low and slow” surface treatment tends to berelatively more effective for a relatively higher silicon-containinglens; a “hot and fast” surface treatment is relatively more effectivefor a relatively lower silicon-containing lens. By “low and slow”surface treatment is meant relatively lower time, higher pressure, andlower wattage, conditions designed to relatively minimize disruption ofcovalent bonds while modifying the substrate, thereby leaving morepolymer at the coating interface with the lens material. Exemplary “lowand slow” conditions for plasma treatment (in a plasma chamber such asused in the following examples) are 100 watts at 0.3 to 0.6 torr, 1-2minutes per side, with 100 to 300 sccm (standard cubic centimeters perminute) in an air/water/peroxide atmosphere (air bubbled through 8%hydrogen peroxide solution in HPLC grade water). By “hot and fast”treatment is meant relatively higher wattage, lower pressure, and longertime, conditions designed to relatively maximize surface modification.Exemplary “hot and fast” conditions for plasma treatment are 400 wattsat 0.1 to 0.4 torr, 10 minutes per side, with 200 to 500 sccm in theabove-indicated atmosphere. The existence of a silicate-containingcoating can be evidenced by a recognizable or statistically significantchange in the surface roughness (RMS), a visual change in the surfacemorphology as evidenced by AFM, such as the formation of surface plates,or by a statistically significant difference in the XPS data for a lensbefore treatment compared to a lens fully processed, notably by adifference in the oxygen and/or silicon content (including theappearance of a silicate peak.) A preferred test for the formation of acoating is 1 to 5% change in oxygen content, within a 95% confidencelevel. As indicated above, if any silicate coating in the fullyprocessed lens (following hydration and heat sterilization) can beformed by either “low and slow” treatment conditions or “hot and fast”treatment conditions, then it is generally possible to obtain a coatingaccording to the present invention by subsequent process adjustments,without undue experimentation, as will be understood by the personskilled in the art. It is noted that the formation of a silicate coatingmerely following plasma treatment is not the test for the applicability,since subsequent delamination during heat sterilization may occur suchthat no coating would be apparent in the fully processed lens.

[0071] Manufacture of the Lens.

[0072] Contact lenses according to the present invention can bemanufactured, employing various conventional techniques, to yield ashaped article having the desired posterior and anterior lens surfaces.Spincasting methods are disclosed in U.S. Pat. Nos. 3,408,429 and3,660,545; preferred static casting methods are disclosed in U.S. Pat.Nos. 4,113,224 and 4,197,266. Curing of the monomeric mixture is oftenfollowed by a machining operation in order to provide a contact lenshaving a desired final configuration. As an example, U.S. Pat. No.4,555,732 discloses a process in which an excess of a monomeric mixtureis cured by spincasting in a mold to form a shaped article having ananterior lens surface and a relatively large thickness. The posteriorsurface of the cured spincast article is subsequently lathe cut toprovide a contact lens having the desired thickness and posterior lenssurface. Further machining operations may follow the lathe cutting ofthe lens surface, for example, edge finishing operations.

[0073]FIG. 1 illustrates a series of manufacturing process steps forstatic casting of lenses, wherein the first step is tooling (1) whereby,based on a given lens design, metal tools are fabricated by traditionalmachining and polishing operations. These metal tools are then used ininjection or compression molding to produce a plurality of thermoplasticmolds which in turn are used to cast the desired lenses frompolymerizable compositions. Thus, a set of metal tools can yield a largenumber of thermoplastic molds. The thermoplastic molds may be disposedafter forming a single lens. The metal molds fabricated during tooling(1) is then used for anterior molding (2) and posterior molding (3) inorder to produce, respectively, an anterior mold section for forming thedesired anterior lens surface and a posterior mold section for formingthe desired posterior lens surface. Subsequently, during the operationof casting (4), a monomer mixture (5) is injected into the anterior moldsection, and the posterior mold section is pressed down and clamped at agiven pressure to form the desired lens shape. The clamped molds may becured by exposure to UV light or other energy source for a certainperiod of time, preferably by conveying the molds through a curingchamber, after which the clamps are removed.

[0074] After producing a lens having the desired final shape, it isdesirable to remove residual solvent from the lens before edge finishingoperations. This is because, typically, an organic diluent is includedin the initial monomeric mixture in order to minimize phase separationof polymerized products produced by polymerization of the monomericmixture and to lower the glass transition temperature of the reactingpolymeric mixture, which allows for a more efficient curing process andultimately results in a more uniformly polymerized product. Sufficientuniformity of the initial monomeric mixture and the polymerized productare of particular concern for silicone hydrogels, primarily due to theinclusion of silicone-containing monomers which may tend to separatefrom the hydrophilic comonomer. Suitable organic diluents include, forexample monohydric alcohols, with C₆-C₁₀straight-chained aliphaticmonohydric alcohols such as n-hexanol and n-n nanol being especiallypreferred; diols such as ethylene glycol; polyols such as glycerin;ethers such as diethylene glycol monoethyl ether; ketones such as methylethyl ketone; esters such as methyl enanthate; and hydrocarbons such astoluene. Preferably, the organic diluent is sufficiently volatile tofacilitate its removal from a cured article by evaporation at or nearambient pressure. Generally, the diluent is included at 5 to 60% byweight of the monomeric mixture, with 10 to 50% by weight beingespecially preferred.

[0075] The cured lens is then subjected to solvent removal (6), whichcan be accomplished by evaporation at or near ambient pressure or undervacuum. An elevated temperature can be employed to shorten the timenecessary to evaporate the diluent. The time, temperature and pressureconditions for the solvent removal step will vary depending on suchfactors as the volatility of the diluent and the specific monomericcomponents, as can be readily determined by one skilled in the art.According to a preferred embodiment, the temperature employed in theremoval step is preferably at least 50° C., for example, 60 to 80° C. Aseries of heating cycles in a linear oven under inert gas or vacuum maybe used to optimize the efficiency of the solvent removal. The curedarticle after the diluent removal step should contain no more than 20%by weight of diluent, preferably no more than 5% by weight or less.

[0076] Following removal of the organic diluent, the lens is nextsubjected to mold release and optional machining operations (7)according to the embodiment of FIG. 1. The machining step includes, forexample, buffing or polishing a lens edge and/or surface. Generally,such machining processes may be performed before or after the article isreleased from a mold part. Preferably, the lens is dry released from themold by employing vacuum tweezers to lift the lens from the mold, afterwhich the lens is transferred by means of mechanical tweezers to asecond set of vacuum tweezers and placed against a rotating surface tosmooth the surface or edges. The lens may then be turned over in orderto machine the other side of the lens.

[0077] Subsequent to the mold release/machining operations (7), the lensis subjected to surface treatment (8), preferably by means of oxidativeRF plasma treatment of the lens surface employing an oxygen-containinggas. Plasma treatment involves passing an electrical discharge through agas at low pressure. The electrical discharge is usually at radiofrequency (typically, 13.56 MHz), although microwave and otherfrequencies can be used. This electrical discharge is absorbed by atomsand molecules in their gas state, thus forming a plasma which interactswith the surface of the contact lens.

[0078] In the prior art, an oxidizing plasma, e.g., employing O₂ (oxygengas), water, hydrogen peroxide, air, etc., or mixtures thereof, has beenused to etch the surface of the lens, creating radicals and oxidizedfunctional groups. Such oxidation is known to render the surface of asilicone lens more hydrophilic; however, the bulk properties of thesilicone materials may remain apparent at the surface of the lens or maybecome apparent after a relatively short period of use. For example,when the oxidation is relatively superficial, the silicone chainsadjacent the lens surface are capable of migrating and/or rotating, thusexposing hydrophobic groups to the outer surface even on a fullyextracted polymer. Also, an oxidized surface may lose the coating due todelamination during further processing steps, including autoclaving. Incontrast, the plasma conditions of the present invention are adjustedand set to obtain the desired combination of ablation and oxidation ofthe surface material, based on careful quality control of the resultingcoating. A relatively thick coating, a permanent barrier between theunderlying silicone materials and the outer lens surface, is therebyachieved in the final product.

[0079] A plasma for the surface modification of the lens is initiated bya low energy discharge. Collisions between energetic free electronspresent in the plasma cause the formation of ions, excited molecules,and free radicals. Such species, once formed, can react with themselvesin the gas phase as well as with further ground-state molecules. Theplasma treatment may be understood as an energy dependent processinvolving energetic gas molecules. For chemical reactions to take placeat the surface of the lens, one needs the required species (element ormolecule) in terms of charge state and particle energy. Radio frequencyplasmas generally produce a distribution of energetic species.Typically, the “particle energy” refers to the average of the so-calledBoltzman-style distribution of energy for the energetic species. In alow density plasma, the electron energy distribution can be related bythe ratio of the electric field strength sustaining the plasma to thedischarge pressure (E/p). The plasma power density P is a function ofthe wattage, pressure, flow rates of gases, etc., as will be appreciatedby the skilled artisan. Background information on plasma technology,hereby incorporated by reference, include the following: A. T. Bell,Proc. Intl. Conf. Phenom. Ioniz. Gases, “Chemical Reaction inNonequilibrium Plasmas”, 19-33 (1977); J. M. Tibbitt, R. Jensen, A. T.Bell, M. Shen, Macromolecules, “A Model for the Kinetics of PlasmaPolymerization”, 3, 648-653 (1977); J. M. Tibbitt, M. Shen, A. T. Bell,J. Macromol. Sci.-Chem., “Structural Characterization ofPlasma-Polymerized Hydrocarbons”, A10, 1623-1648(1976); C. P. Ho, H.Yasuda, J. Biomed, Mater. Res., “Ultrathin coating of plasma polymer ofmethane applied on the surface of silicone contact lenses”, 22, 919-937(1988); H. Kobayashi, A. T. Bell, M. Shen, Macromolecules, “PlasmaPolymerization of Saturated and Unsaturated Hydrocarbons”, 3, 277-283(1974); R. Y. Chen, U.S. Pat. No., 4,143,949, Mar. 13, 1979, “Processfor Putting a Hydrophilic Coating on a Hydrophobic Contact lens”; and H.Yasuda, H. C. Marsh, M. O. Bumgarner, N. Morosoff, J. of Appl. Poly.Sci., “ Polymerization of Organic Compounds in an Electroless GlowDischarge. VI. Acetylene with Unusual Comonomers”, 19, 2845-2858 (1975).

[0080] Based on this previous work in the field of plasma technology,the effects of changing pressure and discharge power on the rate ofplasma modification can be understood. The rate generally decreases asthe pressure is increased. Thus, as pressure increases the value of E/p,the ratio of the electric field strength sustaining the plasma to thegas pressure, decreases and causes a decrease in the average electronenergy. The decrease in electron energy in turn causes a reduction inthe rate coefficient of all electron-molecule collision processes. Afurther consequence of an increase in pressure is a decrease in electrondensity. Providing that the pressure is held constant, there should be alinear relationship between electron density and power.

[0081] In practice, contact lenses are surface treated by placing them,in their unhydrated state, within an electric glow discharge reactionvessel (e.g., a vacuum chamber). Such reaction vessels are commercialavailable. The lenses may be supported within the vessel on an aluminumtray (which acts as an electrode) or with other support devices designedto adjust the position of the lenses. The use of a specialized supportdevices which permit the surface treatment of both sides of a lens areknown in the art and may be used in the present invention.

[0082] The gas employed in the plasma treatment comprises an oxidizingmedia such as, for example, air, water, peroxide, O₂ (oxygen gas), orcombinations thereof, at a electric discharge frequency of, for example,13.56 MHz, suitably between about 100-1000 watts, preferably 200 to 800watts, more preferably 300 to 500 watts, at a pressure of about 0.1-1.0Torr. The plasma treatment time is greater than 4 minutes per side,preferably at least about 5 minutes per side, more preferably about 6 to60 minutes per side, most preferably about 8 to 30 minutes per side foreffective but efficient manufacture. It is preferred that a relatively“strong” oxidizing plasma is utilized in this initial oxidation, e.g.ambient air drawn through a 3 to 30% by weight, preferably 4 to 15%,more preferably 5 to 10% hydrogen peroxide solution, preferably at aflow rate of 50 to 500 sccm, more preferably 100 to 300 sccm.

[0083] Such plasma treatment directly results in a relatively thicksmooth film which may approach the point where the optical clarity isaffected, that is, about 1500 angströms. Preferably, the postplasmacoating thickness should be greater than 1000 angströms, sincesubstantial thickness will be lost during subsequent processing.Following hydration and autoclaving, as further discussed below, thesurface becomes fissured and the thickness may be reduced more than 50percent, even as much as 90 percent or more, from the initial coatingthickness.

[0084] In order to obtain the desired coating, the process parametersmay need to be adjusted in order to obtain a combination of ablation andglass formation that results in the desired coating as subjected afterbeing subjected to further processing steps. The thickness of thecoating is sensitive to plasma flow rate and chamber temperature. Higherflow rates tend to cause more ablation; lower pressures tend to producethicker coatings out of the plasma chamber. However, higher temperaturesmay tend to result in a surface that is less glassy and less cohesive.

[0085] Since the coating is dependent on a number of variables, theoptimal variables -for obtaining the desired or optimal coating mayrequire some adjustment. If one parameter is adjusted, a compensatoryadjustment of one or more other parameters may be appropriate, so thatsome routine trial and error experiments and iterations thereof may benecessary in order to achieved the coating according to the presentinvention. However, such adjustment of process parameters, in light ofthe present disclosure and the state of the art in plasma treatment,should not involve undue experimentation. As indicated above, generalrelationships among process parameters are known by the skilled artisan,and the art of plasma treatment has become well developed in recentyears. The Examples below provide the Applicants' best mode for formingthe coating on a silicone hydrogel lens.

[0086] Subsequent to the step of surface treatment (8) in the embodimentof FIG. 1, the lens may be subjected to extraction (9) to removeresiduals in the lenses. Generally, in the manufacture of contactlenses, some of the monomer mix is not fully polymerized. Theincompletely polymerized material from the polymerization process mayaffect optical clarity or may be harmful to the eye. Residual materialmay include solvents not entirely removed by the previous solventremoval operation, unreacted monomers from the monomeric mixture,oligomers present as by-products from the polymerization process, oreven additives that may have migrated from the mold used to form thelens.

[0087] Conventional methods to extract such residual materials from thepolymerized contact lens material include extraction with an alcoholsolution for several hours (for extraction of hydrophobic residualmaterial) followed by extraction with water (for extraction ofhydrophilic residual material). Thus, some of the alcohol extractionsolution remains in the polymeric network of the polymerized contactlens material, and should be extracted from the lens material before thelens may be worn safely and comfortably on the eye. Extraction of thealcohol from the lens can be achieved employing heated water for severalhours. Extraction should be as complete as possible, since incompleteextraction of residual material from lenses may contribute adversely tothe useful life of the lens. Also, such residuals may impact lensperformance and comfort by interfering with optical clarity or thedesired uniform hydrophilicity of the lens surface. It is important thatthe selected the extraction solution in no way adversely affects theoptical clarity of the lens. Optical clarity is subjectively understoodto be the level of clarity observed when the lens is visually inspected.

[0088] Subsequent to extraction (9), the lens is subjected to hydration(10) in which the lens is fully hydrated with water, buffered saline, orthe like. When the lens is ultimately fully hydrated (wherein the lenstypically may expand by 10 to about 20 percent or more), the coatingremains intact and bound to the lens, providing a durable, hydrophiliccoating which has been found to be resistant to delamination.

[0089] Following hydration (10), the lens may undergo cosmeticinspection (11) wherein trained inspectors inspect the contact lensesfor clarity and the absence of defects such as holes, particles,bubbles, nicks, tears. Inspection is preferably at 10× magnification.After the lens has passed the steps of cosmetic inspection (11), thelens is ready for packaging (12), whether in a vial, plastic blisterpackage, or other container for maintaining the lens in a sterilecondition for the consumer. Finally, the packaged lens is subjected tosterilization (13), which sterilization may be accomplished in aconventional autoclave, preferably under an air pressurizationsterilization cycle, sometime referred to as an air-steam mixture cycle,as will be appreciated by the skilled artisan. Preferably theautoclaving is at 100° C. to 200° C. for a period of 10 to 120 minutes.Following sterilization, the lens dimension of the sterilized lenses maybe checked prior to storage.

[0090] Following the hydration and sterilization steps, thesilicate-containing coating produced by plasma treatment has beenmodified to its final form, in which the coating displays a mosaicpattern of projecting plates surrounded by receding fissures, akin inappearance to closely spaced islands surrounding by rivers. When viewinga 50×50 square micron image by Atomic Force Microscopy, thepeak-to-valley distances (or depth) of the fissures is on averagebetween about 100 and 500 angströms, and the plate coverage (or surfacecoverage) is on average between about 40% and 99%. The depth of thefissures can be considered to be a measurement of the “coatingthickness,” wherein the fissures expose the underlying hydrogel materialunder the silicate-containing, glass-like coating. Preferably, thepeak-to-valley distances of the fissures is on average between 150 and200 angstroms and preferably the plate coverage is on average about 50 %to 99 percent, more preferably 60 to 99%.

[0091] By the term “on average” is meant a statistic average ofmeasurements of controlled lots of lenses taken during commercialmanufacture, based on average measurements of each lens in the opticalzone. Preferably, the average for each lens is calculated based on theevaluation of three 50×50 square micron images per side of the eachlens, as in the examples below. By the term “controlled manufacture” or“controlled process” is meant that the manufactured product isconsistently produced and subject to quality control so that the averagevalues are within a preselected range, or within a preselected range ofspecifications, with respect to fissure depth and plate coverage. Interms of consistency, preferably at least 70%, more preferably at least80%, most preferably at least 90% of the manufactured lenses, with a 95%confidence level, should meet the claimed ranges for coating thicknessand plate coverage. Preferably, the average value, for surface coverageand coating thickness, of the manufactured lenses should be within theclaimed ranges within a 90% confidence level, more preferably within a95% confidence level.

EXAMPLE 1

[0092] This example discloses a representative silicone hydrogel lensmaterial used in the following Examples. The formulation for thematerial is provided in Table 1 below. TABLE 1 Component Parts by WeightTRIS-VC 55 NVP 30 V₂D₂₅ 15 VINAL 1 n-nonanol 15 Darocur 0.2 tint agent0.05

[0093] The following materials are designated above: TRIS-VCtris(trimethylsiloxy)silylpropyl vinyl carbamate NYP N-vinyl pyrrolidoneV₂D₂₅ a silicone-containing vinyl carbonate as previously described inU.S. Pat. No. 5,534,604. VINAL N-vinyloxycarbonyl alanine DarocurDarocur-1173, a UV initiator tint agent 1,4-bis[4-(2-methacryloxyethyl)phenylamino] anthraquinone

EXAMPLE 2

[0094] This Example illustrates a process for the surface modificationof a contact lens according to the present invention. Silicone hydrogellenses made of the formulation of Example 1 above were cast molded frompolypropylene molds. Under an inert nitrogen atmosphere, 45-μl of theformulation was injected onto a clean polypropylene concave mold halfand covered with the complementary polypropylene convex mold half. Themold halves were compressed at a pressure of 70 psi and the mixture wascured for about 15 minutes in the presence of UV light (6-11 mW/cm² asmeasured by a Spectronic UV meter). The mold was exposed to UV light forabout 5 additional minutes.

[0095] The top mold half was removed and the lenses were maintained at60° C. for 3 hours in a forced air oven to remove n-hexanol.Subsequently, the lens edges were ball buffed for 10 seconds at 2300 rpmwith a force of 60 g. The lenses were then plasma treated as follows:The lenses were placed concave side up on an aluminum coated tray andthe tray placed into a plasma treatment chamber. The atmosphere wasproduced by passing air at 400 sccm into the chamber through an 8%peroxide solution, resulting in an Air/H₂O/H₂O₂ gas mixture. The lenseswere plasma treated for a period of 8 minutes (350 watts, 0.5 Torr). Thechamber was then backfilled to ambient pressure. The tray was thenremoved from the chamber, the lenses flipped over, and the procedurerepeated to plasma treat the other side of the lenses.

[0096] Lenses were analyzed directly from the plasma chamber and afterfull processing. Full processing included, following plasma treatment,extraction, hydration and autoclave sterilization. Extraction employedisopropanol at room temperature for 4 hours (during commercialmanufacture a minimum of 48 hours following by extraction in water atabout 85° C. for 4 hours is preferred). The lenses were then immersed inbuffered saline for hydration. Autoclaving was carried out with thelenses, within vials, immersed in an aqueous packaging solution.

[0097] The plasma chamber was a direct current DC RFGD chambermanufactured by Branson GaSonics Division (Model 7104). This chamber wasa cold equilibrium planar configuration which had a maximum power of 500watts. All lenses were prepumped to 0.01 Torr prior to any plasmatreatment from residual air in the chamber. This process reduced therelative treatment level of the polymer by controlling gas pressure.

[0098] All lenses in this study were analyzed as received. Thepre-plasma and post plasma lenses were analyzed dry. The fully processedlenses were removed from the vials and desalinated in HPLC grade waterin a static fashion for a minimum of 15 minutes. Three lens posteriorsand three lens anteriors from the pre-plasma, post plasma, and fullyprocess lenses of each lot were analyzed by X-ray PhotoelectronSpectroscopic (XPS).

[0099] The XPS data was acquired by a Physical Electronics [PHI] Model5600 Spectrometer. To collect the data, the instrument's aluminum anodewas operated at 300 watts, 15 kV, and 20 mA. The A1 Kα line was theexcitation source monochromatized by a toroidal lens system. A 7 mmfilament was utilized by the X-ray monochromator to focus the X-raysource which increases the need for charge dissipation through the useof a neutralizer. The base pressure of the instrument was 2.0×10-10 Torrwhile during operation it was 1.0×10-9 Torr. A hemispherical energyanalyzer measures electron kinetic energy. The practical sampling depthof the instrument, with respect to carbon, at a sampling angle of 45°,is approximately 74 Angströms. All elements were charge corrected to theCH_(x) peak of carbon binding energy of 285.0 eV.

[0100] Each of the plasma modified specimens were analyzed by XPSutilizing a low resolution survey spectra [0-1100 eV] to identify theelements present on the sample surface. The high resolution spectra wereperformed on those elements detected from the low resolution scans. Theelemental composition was determined from the high resolution spectra.The atomic composition was calculated from the areas under thephotoelectron peaks after sensitizing those areas with the instrumentaltransmission function and atomic cross sections for the orbital ofinterest. Since XPS does not detect the presence of hydrogen or helium,these elements will not be included in any calculation of atomicpercentages. The atomic composition data has been outlined in Table 2.TABLE 2 Oxygen Nitrogen Carbon Silicon Fluorine Experiment 1 pre-plasmaAVG 18.6 6.2 64.7 10.5 0.0 STDEV 1.2 0.4 1.3 0.7 0.0 post-plasma AVD47.6 3.1 29.0 18.9 1.6 STDEV 1.3 0.2 1.3 0.3 0.1 fully AVG 19.5 7.8 64.87.9 0.0 processed STDEV 0.8 0.3 0.9 0.3 0.0 Experiment 2 pre-plasma AVG18.0 6.0 65.2 10.8 0.0 STDEV 0.5 0.5 0.9 0.7 0.0 post plasma AVG 49.42.7 26.5 20.1 1.4 STDEV 1.5 0.3 2.0 0.9 0.2 fully AVG 19.6 7.7 64.8 7.80.0 processed STDEV 0.3 0.3 0.8 0.7 0.0 Experiment 3 pre-plasma AVG 18.16.0 66.8 9.1 0.0 STDEV 1.2 0.7 1.5 0.8 0.0 post plasma AVG 50.2 1.7 22.023.1 2.6 STDEV 1.3 0.3 1.9 1.0 0.5

[0101] Each experiment involved testing 6 lens from the sample lot of 50to 100 lenses. The survey spectra for the pre-plasma lenses ofExperiments 1 to 3 contain photoelectron peaks indicative of oxygen,nitrogen, carbon, and silicon. The silicon 2p3/2 peak position (102.4eV) indicates that the detected silicon on the surface originated fromderivatives of silicone. The survey spectra for the post-plasma lensesof the Experiments 1 to 3 contain photo-electron peaks indicative ofoxygen, nitrogen, carbon, silicon, and fluorine. The fluorine is aby-product of the plasma ablation of the Teflon runners which supportthe trays used to hold the lenses. The silicon 2P3/2 photoelectron peakposition (103.7 eV) indicates that the detected silicon on the surfaceoriginated from silicates, verifying the presence of a coating. Asevidenced, slight differences in the elemental analyses for differentexperiments may result from slight variations in the plasma processingparameters, location in the chamber, or as a result of inherent surfaceproperties of the lenses of this particular lot.

[0102] In addition, Atomic Force Microscopy (AFM) was employed to studythe morphology of the contact lens surfaces. AFM works by measuringnano-scale forces (10⁻⁹ N) between a sharp probe and atoms on the lenssurface. The probe is mounted on a cantilever substrate. The deflectionof the cantilever, measured by a laser detection system, is processed togenerate height information. While gathering height information, theprobe is rastered in the x-y plane to generate a three dimensionaltopographical image of the lens surface. In the optical zone of eachlens, three images were sampled on both sides of the lens.

[0103] The fraction of the lens surface that is covered by the coatingis referred to as “plate coverage” or “surface coverage.” Thismeasurement is sometimes easily made by looking at a histogram of thesurface heights. However, when the coating is too thin, (<10 nm) thecoverage is not attainable from the histogram. When this occurs, the AFMimage in question is compared to previous AFM images of which the exactcoverage is known. When this visual method is used, the coverage isestimated and correct to within ±10%.

[0104]FIG. 2 is an Atomic Force Microscopy (AFM) topographical imageshowing a plasma-treated lens before further processing by hydration andautoclaving. The image shows a lens coating with a smooth surface (100%surface coverage) very similar in appearance to the surface beforeplasma treatment. This is because most plasma coatings are conformal tothe original surface. As evident, the surface is not perfectly smooth.The surfaces show some fine multidirectional scratches due to toolingmarks.

[0105]FIG. 3, for comparison to a lens surface according to the presentinvention, is an Atomic Force Microscopy (AFM) photograph showing anautoclaved plasma-treated lens (fully processed) after a plasmatreatment time period of only 4 minutes per side but otherwisecomparable to the process conditions of this Example. The coatingthickness is only 4+/−2 nm thick, with only about 20% coverage. Thecoloring in the image represent distinct heights on the surface. Thelighter areas correspond to the raised features, while the dark areascorrespond to the recessed features. In the image of FIG. 3, it isapparent that the coating has cracked and flaked away, exposing thesurface of the lens, therefore showing a relatively smooth surface withbarely visable plates.

[0106]FIG. 4 is an Atomic Force Microscopy (AFM) image of anplasma-treated lens following extraction with isopropanol. The lensthickness is about 100 nm (which will be reduced during subsequentautoclaving), and the surface coverage is about 50 percent. Since theAFM images are in the dry state, the surface coverage of the extractedand fully processed lenses are comparable.

[0107]FIG. 5 is an Atomic Force Microscopy (AFM) topographical image(50×50 square microns) showing a hydrated and autoclaved plasma-treatedlens (fully processed according to the present invention) after a timeperiod of 8 minutes, showing distinct plates with excellent surfacecoverage. The coating thickness is about 10+/−2 nm thick (100 angströms)with about 95 percent surface coverage.

[0108] The average depth of the fissures in the coating (also referredto as the “coating thickness”) were directly measured using AFMsoftware. The thickness of 3-5 islands (arbitrarily selected) in eachpicture is measured and averaged to yield an overall coating thicknessfor each image. Preferably, the RMS roughness of the fully processedlens is less than about 50 nm, more preferably about 2 to about 25 nm,most preferably 5 to 20 nm.

[0109] This comparison shows that, in addition to such other parametersas pressure or air flow rate, the time period of the plasma treatment isa significant controlling parameter during plasma treatment in order toobtain the desired coating.

COMPARATIVE EXAMPLE 3

[0110] Silicon hydrogel lenses of the formulation in Example 1 abovewere plasma treated for a period of time of 4 minutes per side and usedin a clinical study. Due to variance in the lens surface topography someof the lots showed a smooth surface without any evidence of plates wheninspected employing surface imaging by Atomic Force Microscopy (AFM), inwhich a 50×50 micron square image was made of a typical area of the lensequal to 1.5×10⁸ square microns. Thirteen lots were examined showing afull range of surfaces and were classified as “Mosaic to Transitional”(hereafter “Mosaic”) and “Transitional to Smooth” (hereafter “Smooth”).Approximately 42 percent of the lenses exhibited a Smooth Surface. Bythe term “Smooth,” with respect to the lens, is meant a lens surfacethat does not show the silicate plates surrounded by valleys orfissures, similar to closely spaced islands surrounded by rivers. TheSmooth Lenses also included lenses with a surface coverage of less than30 percent and a valley depth of less than about 50 angstroms. TheMosaic lens were those which showed more than 30 percent coverage and avalley depth greater than 50 angstroms.

[0111] In order to correlate surface characteristics to clinicalperformance, the lenses used in the clinical study were sorted by degreeof deposition based on information provided by practitioners involved inthe study. The Grade Levels were from 0 to 4 corresponding to increasinglevels of deposition via slit lamp analysis. For Grades 0 and 1, wherethe number of patients was high, the lenses were separated so that halfof the Grade could be tested for lipid and the rest for protein. Sincethe number of lenses in Grades 2, 3 and 4 were much lower, these lenseswere cut in half (using a scalpel and gloves) so that each lens could betested for protein and lipid. Data generated on these lenses was doubledin order to represent deposition on the entire lens. The lenses wereworn for 3 months with enzyme cleaning at the end of a week of wear andthen disinfected with ReNu MPS solution overnight. In some cases, thelens was replaced before the 3 months due to specified reasons. In allother instances, the lens was worn for the entire study. After 3 months,all lenses were shipped (in a dry state) and stored in a refrigeratorupon arrival.

[0112] To further correlate surface characteristics to depositionproperties (composition), protein and lipid analysis of the depositswere conducted. Protein Analysis was done using the calorimetric BCAanalytical method (Sigma). The method employs the protein inducedreduction of Cu(II) to Cu(I). A purple complex (A_(MAX)=562 nm) is thenformed following the addition of Bicinchoninic acid (BCA) to the reducedcopper. The intensity of the complex is shown to be directlyproportional over the protein concentration range 5 μg/ml to 2000 μg/ml.Following incubation at 37°, the rate of color development is slowedsufficiently to allow large numbers of samples to be done in a singlerun. The standard protein solution utilized was BSA with a standardconcentration range of 0-200 μg. The analytical protocol was as follows:

[0113] 1) In the preparation of the standards, an unworn lens is takenout of vial, left to air dry and then placed in a plastic centrifugetube along with standard BSA solution. Worn lenses (also air dried) arealso placed in centrifuge tubes. A mixture of BCA/Copper (II) Sulfatesolution is then added to the dried lenses.

[0114] 2) Tubes are then placed in a water bath at 37° for 15 minutes.After incubation, the purple complex develops.

[0115] 4) Samples and standards are read at 562 nm.

[0116] 5) Protein concentration is then determined from a Standard plotof Absorbence vs.

[0117] Concentration (μg).

[0118] 6) Protein results reported represent total amount of boundprotein.

[0119] Gas Chromatography (GC) is the method by which total lipidconcentration was determined. Tripalmitin (C₁₆) was used as the standardbased on previous GC runs of C₁₂-C₂₂ chain length lipids which allshowed similar retention times. Stock solution of standards was 1 mg/mlTripalmitin in Methylene Chloride where the concentration range for thestandards was 0-100 μg. The analytical protocol involved the followedsteps:

[0120] The same protocol as above was used for the standards wherein anunworn lens is placed in a glass test tube with the standard solution.Otherwise, the protocol was as follows:

[0121] 1) When the hexane is added to the lens (with heat), the lenswill dissolve and eventually precipitate to the bottom of the tube. Twophases will form. The bottom layer is cloudy (MeOH layer) and the toplayer (hexane layer) is clear. The hexane layer is extracted out. Theextraction of samples and standards is done twice. The fact that thelens dissolves during this procedure allows one to determine the totalamount of lipid both on the surface and potentially imbedded into thelens matrix.

[0122] 2) A stream of N₂ is used to blow off the hexane from the tubes.The samples and standards are then re-suspended in 50 μl of hexane.

[0123] 3) Hexane is run through the GC (2 μl) to make sure peaks comeoff with the appropriate retention times.

[0124] 4) A 2 μl amount from each tube is then injected into the GC. Thesyringe was cleaned 10-14 times with hexane between each run. Theretention time of the lipids corresponds to chain length. C₈-C₁₂, C₁₂,C₁₄ and C₁₆-C₁₈ come off at increasing intervals. The GC is a CapillaryCG 30 ft HPR1 column attached to an FID detector (mass), so mass can beread corresponding to the peaks (in μg).

[0125] 5) The standard curve of tripalmitin plots the Peak Area vs. TheAmount Lipid (μg).

[0126] Based on the practitioner grading scale, 86% of the patientsinvolved in the study were categorized in Grades 0-2, reflecting minimalto no surface deposits. The average Protein concentration among theseGrades was 34.2 μg and the average amount of Lipid was 17.5 μg. Thedetailed results of protein and lipid analysis in the study are shown inTable 3 below: TABLE 3 Grade 0 Grade 1 Grade 2 Grade 3 Grade 4 (84*)(46*) (28*) (19*) (5*) Average 24.7 μg 42.7 μg 35.3 μg 39.7 μg 43.4 μgProtein Concentration: Range: 0-105 μg 8.6-80 μg 2.6-75 μg 0-92 μg 25-60μg Average 0 μg 16.0 μg 19.1 μg 40.1 μg 65.0 μg Lipid Concentration:Range: — 0-51 μg 0-61.4 μg 0-92 μg 30-96 μg

[0127] The range of protein and lipid concentrations observeddemonstrates the individual variability in deposition levels as well asthe variability in the practitioners' assessment of Grade of deposition.Overall, protein levels among all of the Grades remains relativelyconstant (˜35-40 μg) except for Grade 0 where the number is a bit lower(25 μg). Lipid deposition, however, consistently increases with Gradeindicating that heavy soilers seem to be depositing on average morelipid than protein. Of the 24 patients who were categorized as havingGrade 3 and 4 deposition, 5 had experienced discomfort. There was nocorrelation observed between the age (wear time) of the lens and thedegree of deposition.

[0128] The following table shows the distribution of the lots among theGrades of deposition demonstrating the relative susceptibility of lensesin particular lots to deposition. TABLE 4 Lens Lot #Lenses #Lenses#Lenses #Lenses #Lenses # Grade 0 Grade 1 Grade 2 Grade 3 Grade 4 1 8 64 3 1 2 7 5 1 4 1 3 8 4 0 3 4 8 2 1 1 5 12 5 0 3 6 12 3 1 0 7 10 1 1 3 28 6 2 2 1 9 5 2 2 5 10 2 2 1 2 1 11 4 6 5 3 12 6 5 1 0 13 6 3 2 1

[0129] Correlating the lens surface to the deposition, the results wereas follows: TABLE 5 MOSAIC SMOOTH Lot Surface % 2-4 Lot Surface % 2-4 32 9% 2 3 11% 4 1.75 5% 5 2.75 15% 6 2.25 6% 7 2.5 17% 8 1 7% 8 3 16% 102 14%  9 2.75 13% 12 2 7% 11 3 11% 13 2.75 13%

[0130] These results show that for plasma treated lenses showing“mosaic” surface characteristics similar to that of FIG. 3 from Example2 above, the percentage of lenses with a deposit rating of greater than2 was 8%, whereas for similarly plasma treated lenses that did not showthe “mosaic” surface characteristics of FIG. 2 (for example, like thelens shown in FIG. 4), the percentage of lenses with a deposit rating ofgreater than 2 was 14%, showing a statistically significant superiorityfor the mosaic pattern.

EXAMPLE 4

[0131] To show the change in wetting properties of lenses according tothe present invention, contact angle measurements were made of anuntreated lens (before plasma treatment), a plasma treated lens(immediately after plasma treatment) and after fully processing(including hydration and heat sterilization). The contact angle wasmeasured as follows. A platinum wire (Pt) was employed to minimizecontamination. The Pt wire was pulled across a flame over a Bunsenburner until the wire reached a dull red (orange) glow, in order toensure that the water (HPLC grade) employed in the test was exposed to afresh, clean metal surface, free from contamination. About 2 microlitersof water was transferred from its bottle to the wire, which processinvolved tipping of the bottle so that the maximum amount of wire wasunder the liquid. The water on the wire was transferred, withoutdragging along the surface, to a lens made from the material ofExample 1. Once transferred, an NRL-100 Rhamé-Hart Contact AngleGoniometer was employed to measure the contact angle. The baseline wasset by adjusting the stage height until the baseline was drawn betweenthe bottom of the drop and its own reflection. After finding thebaseline, the contact angle formed by the drop was measured on the rightand on the left. Another drop of water was added to the first drop, andthen the contact angles were recalculated for the left and right sides.All four measurements were averaged. Employing this measurement, thelens surface before treatment exhibited a water contact angle of about90 dynes/cm. Following plasma treatment, the water contact angle was 0dynes/cm. Following heat sterilization, the fully processed lensexhibited a contact angle of 72.4+/−2 dynes/cm. All measurements were ondry lenses.

[0132] Many other modifications and variations of the present inventionare possible in light of the teachings herein. It is thereforeunderstood that, within the scope of the claims, the present inventioncan be practiced other than as herein specifically described.

1. A method for treating the surface of a silicone hydrogel contact lensby a controlled manufacture comprising the following steps: (a) plasmatreating the lens with an oxygen-containing atmosphere for more than 4minutes per side, at a wattage of 100 to 1000 watts and a pressure of0.1 to 1.0 torr, to produce a silicate-containing coating, (b) hydratingthe lens by immersing the lens in an aqueous solution, whereby theamount of water absorbed by the lens is at least five percent by weightof the lens material, (c) subjecting the hydrated lens to heatsterilization, whereby the heat sterilized lens has asilicate-containing coating characterized by a mosaic pattern ofprojecting plates surrounded by receding fissures when viewing a 50×50square micron AFM image, wherein the depth of the fissures is on averagebetween about 100 and 500 angströms and the plate coverage is on averagebetween about 40 to 99 percent.
 2. The method of claim 1, wherein theplasma treatment in step (a) is 300 to 500 watts for a period of 6 to 60minutes per side.
 3. The method of claim 1, wherein the plasma treatmentin step (a) is for a period of 8 to 30 minutes per side.
 4. The methodof claim 1, wherein step (b) swells the lens 5 to 25 percent.
 5. Themethod of claim 1, where in the autoclaving is 100° C. to 200° C. for aperiod of 10 to 120 minutes.
 6. The method of claim 1, wherein thefissure depth is on average between about 150 and 200 angstroms.
 7. Themethod of claim 1, wherein the plate coverage is on average betweenabout 60 to 80 percent.
 8. The method of claim 1, wherein at least 80percent of the lens in a commercially manufactured lot are within thesaid ranges for the depth of the fissures and plate coverage.
 9. Themethod of claim 8, wherein at least 90 percent of the lenses are withinsaid ranges.
 10. The method of claim 1, wherein the silicone hydrogelcomprises in bulk formula 5 to 50 percent by weight of one or moresilicone macromonomers, 5 to 75 percent by weight of one or morepolysiloxanylalkyl (meth)acrylic monomers, and 10 to 50 percent byweight of a hydrophilic monomer
 11. The method of claim 10, wherein thesilane macromonomer is a poly(organosiloxane) capped with an unsaturatedgroup at two or more ends.
 12. The method of claim 10 wherein the silanemacromonomer is a silicon-containing vinyl carbonate or vinyl carbamateor a polyurethane-polysiloxane having one or more hard-soft-hard blocksand end-capped with a hydrophilic monomer.
 13. The method of claim 1,wherein the polysiloxanylalkyl (meth)acrylic monomers ismethacryloxypropyl tris(trimethyl-siloxy)silane.
 14. The method of claim1, wherein the hydrophilic monomer is selected from the group consistingof unsaturated carboxylic acids, acrylic substituted alcohols, vinyllactams, acrylamides, vinyl carbonate or vinyl carbamate, oxazolonemonomers, and mixtures thereof.
 15. The method of claim 14, wherein thehydrophilic monomer is selected from the group consisting of methacrylicand acrylic acids, 2-hydroxyethylmethacrylate and2-hydroxyethylacrylate, N-vinyl pyrrolidone, methacrylamide,N,N-dimethylacrylamide, and mixtures thereof.